Generally, this type of motor has a brushless DC motor configuration, many of which are configured in that a stator is molded by resin material in order to assure excellent electric insulation. Also, the bearing employed is a slide bearing for simplifying the structure, and lubricating oil is supplied to the bearing for prolonging the life.
FIG. 5 is a sectional view of a conventional fan motor, and FIG. 6 is a sectional view of another conventional motor.
In the motor shown in FIG. 5, nearly cylindrical housings 51 made of aluminum metal are arranged at upper and lower positions. Each of both housings 51 accommodates a slide bearing 52. These two bearings 52 rotatably support rotary shaft 53. Inside the upper and lower end portions of both housings 51 are respectively stored oil retainers 54 for supplying lubricating oil to these bearings 52. Outside the housing 51 are installed core 55 and drive coil 56, and these are molded by resin material to form casing member 57. Stator 58 is configured in this way.
Cover 59 is attached by press-fitting or the like to both ends of the housing 51. Also, oil barrier 60 corresponding to the bearing 52 on the fan load side is attached to the rotary shaft 53. Cup-like rotor 62 is coupled with the rotary shaft 53. The rotor 62 has magnet 61 opposing to the core 55 of stator 58.
In FIG. 5, an electric circuit is formed on printed wiring board 63. Motor casing 64 is disposed outside the rotor 62. Fan blade 65 is fitted to the rotary shaft 53.
The conventional motor shown in FIG. 5 is small-sized and configured so as to assure excellent corrosion resistance, moisture resistance, and electric insulation, which is also able to prolong the life with the oil supplied from the oil retainer 54. However, the number of parts used is increased because of using two bearings 52 and two oil retainers 54, and also, the structure is complicated causing the cost to be increased.
Also, FIG. 6 is a sectional view of another conventional motor that is disclosed in Japanese Laid-open Patent H8-98447.
The rotor of this motor is an epicyclic rotor which rotates outside the stator, and the stator has a single slide bearing in the housing, and at the fan load side of the housing is disposed a stop member and a housing lid. The motor is less in the number of parts used as compared with the conventional motor shown in FIG. 5.
That is, as shown in FIG. 6, in stator 66, a single slide bearing 68 is arranged in the housing 67 which is formed from resin having a generally cylindrical shape. Rotary shaft 79 is rotatably supported by the bearing 68. At the fan load side of the housing 67 is arranged the stop member 69 of the rotary shaft 79. Upper end projection 70 of the stop member 69 is fitted in groove 71 of the rotary shaft 79. Outside the housing 67 are disposed the core 72 and drive coil 73 which are held by insulator 74 fitted by ultrasonic welding to the housing 67. And, a part of the insulator 74 serves as housing lid 75. The rotor 76 is an epicyclic rotor which rotates outside the stator 66. Magnet 77 is fitted to the rotor 76, which is opposed to the core 72. The circuit board 78 serves to detect the pole position of the magnet 77 of the rotor and to properly feed power to the drive coil 73.
In the motor shown in FIG. 6, since a single slide bearing 68 is employed, the motor structure is relatively simple, less in the number of parts used, and easy of positioning of the parts, and also, the assembling work can be easily performed.
However, since a casing member using resin material is not employed for this motor, when it is used under high humidity environment such as in a refrigerator, there arises a problem such as generation of rust or poor electric insulation. Also, when the lubricating oil of the bearing 68 is used up, the oil cannot be replenished, and the life cannot be prolonged, and moreover, maintenance cannot be executed by removing the rotary shaft 79 and rotor 76.
Then, as to the stator of the motor configured as shown in FIG. 6, for suppressing the generation of rust and improving the electric insulation, it is possible to form the casing member just by molding resin material but, in that case, there arise the following problems.
For example, there is a possibility that the ultrasonic welding portions are not strong enough to endure stresses applied thereto during molding. Further, there is a possibility of oil leakage because of no oil retainer for the lubricating oil, and there is a problem that the leaked oil becomes liable to be absorbed by the casing member being a molded resin material, and therefore, it is unable to prolong the life. Also, since the rotary shaft and rotor cannot be easily removed, there arises such problem that the oil cannot be externally supplied.
Accordingly, it is not preferable to use a motor having such structure as a mold type motor.